1. Field of the Invention
The present invention relates to a method and a system for shift control of an automatic transmission and more particularly to a method and a system for shift control of an automatic transmission to relieve shift shock by reducing engine torque at the time of a kick down skip shift.
2. Description of the Invention
In general, an automatic transmission selects a shift pattern to optimize shift in relation to a running state of an auto vehicle and operates various solenoid valves according to the shift pattern to change the combination of planetary gears, thus achieving a desired shift. In the course of the shift, shift shock is generated by a change in the combination of planetary gears causing a change in the torque of an output axis.
Accordingly, in order to relieve the aforementioned shift shock, there have been used methods to reduce engine torque at the time of a shift. For instance, at the time of a kick down skip shift, the shift shock is relieved by starting to reduce engine torque when the rotation number of a turbine reaches its preset value and stopping to reduce engine torque when a preset period of time lapses.
When a driver steps on a brake pedal and makes a sudden stop of a vehicle running at a fourth speed stage to achieve a 4-3 shift (a shift from stage 4 to stage 3) (hereinafter referred to as the 4-3 shift before stop), conditions for a kick down skip 3-1 shift are satisfied with a tip-in manipulation of stepping on an accelerating pedal to accelerate the vehicle. As a result, the kick down skip 3-1 shift is completed right after the 4-3 shift. At this time, the 3-1 shift is achieved right after the 4-3 shift before stop by reducing engine torque on the basis of the same engine torque reduction starting point and engine torque reduction maintaining time as those for the kick down skip 3-1 shift during a normal running state of the vehicle. However, there is a problem of significantly bringing about shift shock in the conventional engine torque reduction method because the reduction of engine torque cannot be made at an adequate point of time.
It is an object of the present invention to solve the aforementioned problems and provide a method and a system for shift control of an automatic transmission, the apparatus which can relieve shift shock of a kick down skip shift generated by re-acceleration during a sudden stop of a vehicle by determining an engine torque reduction starting point and an engine torque reduction maintaining time on the basis of a vehicle deceleration rate at the time of the 4-3 shift before stop when the kick down skip 3-1 shift is made after the 4-3 shift before stop has been completed by getting the kick down skip 3-1 shift to be satisfied by the tip-in manipulation during the 4-3 shift before stop; and by reducing engine torque on the basis of the determined engine torque reduction starting point and engine torque reduction maintaining time.
In order to accomplish the aforementioned object of the present invention, there is provided a system for shift control of an automatic transmission, the system comprising:
vehicle running status detecting means for detecting the running status of a vehicle;
shift control means for outputting a control signal to perform a kick down skip 3-1 shift if conditions for the kick down skip 3-1 shift are satisfied with a tip-in manipulation during the 4-3 shift before stop by receiving an input of a signal detected by the vehicle running status detecting means, and for outputting an engine torque reduction requesting signal on the basis of an engine torque reduction starting point and an engine torque reduction maintaining time determined according to a vehicle deceleration rate of the 4-3 shift before stop at the time of the kick down skip 3-1 shift;
transmission driving means for carrying out a shift by supplying or stopping the oil pressure discharged and supplied from an oil pump according to a control signal output from the shift control means;
engine control means for outputting a predetermined control signal to reduce engine torque according to an engine torque reduction requesting signal output from the shift control means; and
engine driving means for reducing engine torque according to the control signal output from the engine control means.
In addition, there is provided a method for shift control of an automatic transmission in accordance with the present invention, the method comprising the steps of:
discriminating whether conditions for a kick down skip 3-1 shift are satisfied with the tip-in manipulation during the 4-3 shift before stop;
reducing an engine torque, when the conditions for the kick down skip 3-1 shift are satisfied, according to a reduction starting point determined on the basis of the vehicle deceleration rate during the 4-3 shift before stop; and
returning an engine torque to its original value if the engine torque reduction maintaining time determined on the basis of the vehicle deceleration rate during the 4-3 shift before stop elapses